Why do you need a global listing type
A global listing type can be used in explore page to display listing results from all other listing types on your explore page. It can also be used in the 27 > map widget to display all listings from all types in the map.
What not to use it for
A global listing type should not be used in add listing page, it’s strictly used for filtering purposes not to add listings
How to create a global listing type
Add a listing type in wp-admin > listing types > add new > name it “All” or something similar.
Go general tab > other
Enable the option “Global listing type”
You should also setup the search filters in the “Search form” tab and click save.
How to add it to explore page
Edit your explore page using Elementor and add the listing type as the first option in explore widget settings. More about that here